Some fats can smooth the path to heart health
The Irish Times
Health Supplement, p. 13
2 June 2009
DOES IT WORK? Omega fats and heart disease
Cardiovascular disease is the leading cause of death in Western countries. The term covers a group of diseases that includes atherosclerosis (‘clogged’ arteries), heart attack and stroke. Diet plays an important role in cardiovascular disease, with much attention focused on fats and omega fatty acids in particular. Dietary fats and lipids are made from various fatty acids which are then released when digested. Initial discussions of the effects of fatty acids on health focused on whether they were of plant or animal origin, but the situation is now known to be much more complicated. Dairy products have been found to contain over 400 different fatty acids. Omega fatty acids tend to be found in plant and fish oils.
Although fats tend to be viewed negatively, all cells of the body require fats to build and maintain healthy membranes. Fatty acids are important sources of energy and are used to make a number of other compounds essential for good health. This is part of the reason why fatty acids are believed to be involved in many conditions that affect various parts of the body.
Chemically, fatty acids contain long chains of carbon atoms with varying numbers of double bonds. Saturated fatty acids are those with no double bonds and they tend to be found in animal fats. Unsaturated fatty acids contain at least one double bond, and polyunsaturated fatty acids contain a number of double bonds. Among the polyunsaturated fatty acids, omega-3 and omega-6 fatty acids have drawn much recent attention. Their name derives from the location of the first double bond on the carbon chain. To complicate things further, both types of omega fatty acids come in short-chain and long-chain forms and their effects in the body appear to be somewhat different.
Evidence from studies
Numerous studies have been conducting on the role of omega fatty acids in cardiovascular disease. Possibly the most important thing coming out of these studies is a better understanding of the complicated interactions. No longer can simple instructions to reduce animal fats or increase certain fatty acids be given. In addition, the same dietary advice regarding fatty acids does not apply equally to everyone because of genetic and other lifestyle variables.
Much of the evidence around dietary fatty acids comes from epidemiological studies. In these studies, people report their activities, including diet, and records are kept of their health and any illnesses. Early studies noted that people who ate larger amounts of saturated (animal) fats had higher risks of cardiovascular disease. A limitation with epidemiological studies is that they reveal connections, but not causation. The effects could be caused by other factors, including other dietary and lifestyle factors. Other studies have shown that when people reduce their saturated fat intake, their risk of heart disease is lowered. However, weight reduction and increased physical activity must accompany the dietary changes for people to get the beneficial effects, especially for those with any history of cardiovascular disease.
Omega-6 fatty acids are polyunsaturated. Early studies found that increasing their intake reduced the risk of cardiovascular disease. However, this trend changes when people take in high doses of omega-6 fatty acids. High intakes promote oxidation and other changes which can be harmful. Most recent studies show that the ratio of omega-6 to omega-3 fatty acids in the diet is very important.
Omega-3 fatty acids come in short-chain (alpha-linolenic acid, ALA) and long-chain forms like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is found mostly in plants while EPA and DHA are found mainly in fish oils. Numerous studies have shown beneficial effects from increasing the amount of omega-3 fatty acids in the diet, either through supplements or by eating fish at least weekly. A small group of studies conducted in India have shown spectacular benefits from diets high in omega-3 fatty acids. However, allegations of fraud have been made around these studies in an-ongoing debate involving the British Medical Journal. More moderate benefits have been confirmed, again with the ratio of omega-6 to omega-3 being most important.
Omega fatty acids are important in the diet. The average Western diet has a ratio of omega-6 to omega-3 of about 15:1. Ratios of around 5:1 have been shown to have beneficial effects on the risk of cardiovascular disease, with ratios of 2:1 lowering the risks of other diseases. Some foods and supplements are available with this type of ratio. However, other risk factors for cardiovascular disease and other lifestyle factors are important. People who are active, not over-weight and without a history of cardiovascular disease can tolerate a diet with a mixture of saturated and unsaturated fats. What is most important is a balanced intake. Given the average Western diet, however, many would benefit from increasing the amount of omega-3 fatty acids and limiting the amount of omega-6 fatty acids, especially as other risk factors for cardiovascular disease increase. Other factors such as fruit, vegetable and fibre intake, as well as physical activity, must be combined for an overall heart-healthy lifestyle.